In such centralized vacuum systems, the vacuum assembly together with its dust reservoir is located in a utility area and the tube terminating in the housing is part of a network of tubes connecting the central power unit to wall valves located in the areas to be cleaned. Each wall valve is sealed by a hinged lid and receives the rear nozzle of a hose whose front nozzle, equipped with a handle, receives a rigid wand or cleaning tool.
In the majority of current systems, the central power unit is turned on and off by microcontacts located in each wall valve and by a low-voltage electrical circuit connecting each wall valve to the power unit. Thus, when the user inserts the rear nozzle of the vacuum hose into a wall valve, the power to the electric motor in the power unit is turned on; withdrawing the nozzle cuts off the power.
The low-voltage electrical circuit is either mounted next to the vacuum tubes or installed inside these tubes, and always requires a long installation time, to which is added the time required to hook up the wall valves and to check the electrical connections. Consequently, this control mode results in a rather high installation cost, plus the cost of the electrical equipment that must be installed, comprising a transformer, relays at the power unit, and the various contacts in the wall valves. Another disadvantage of this type of control arises from the necessity to unplug the hose to open the control circuit and stop the power unit. In addition, several types of systems are known comprising a start-stop button on the hose handle, with electrical conductors as an integral element of the hose. Hoses of this kind are little used, however, because they are heavier and even more awkward than traditional ones. The same remote control method for operating the vacuum assembly is provided on certain portable vacuum cleaners. Here again, it has resulted in significant extra expense and increased weight.
Documents U.S. Pat. No. 3,669,145 and GB-A-2 015 652 each describe a centralized vacuum system comprising a main vacuum turbine and a system furnishing a secondary vacuum when the turbine is not operating. Opening a switch valve on a vacuum hose in the system changes the negative pressure to supply pneumatic information causing the main vacuum turbine to operate.
Document EP-A-0 156 011 relates to a control device for a portable vacuum cleaner, especially by action on the handle of a dust vacuum hose. This device comprises a small duct parallel to the main hose and serving to carry a pneumatic pressure wave from the handle to the vacuum assembly, causing the turbine to start if it is stopped, or to stop if it is running. In addition, negative pressure waves transmitted through the small duct from the handle enable the vacuum level to be adjusted. In view of its complexity, a control device of this kind is not applicable to a central vacuum or ventilation system.